614 



ADDENDA. 



zones, that solid glaciers descend to the sea in low latitudes ; I might have 

 added that it is in this same hemisphere, that the icebergs, which have 

 been formed in the Polar Regions, are drifted furthest from their birth- 

 place. Horsbiirgh ( Philosoph. Transact., 1830) describes several great ice- 

 bergs seen by a ship, in her passage to India, in 35° 50' S. : that is, far to 

 the northward of the latitude, where tree-ferns, arborescent grasses, para- 

 sitical orchideous plants, and even palm-trees grow ; and within sixty miles 

 of the land, where the rhinoceros, elephant, hippopotamus, lion, and hyena, 

 are very numerous. 



Page 289. 



Until lately I was not aware that there were sufficient data to speak 

 with some precision of the southern limits of erratic blociis in the northern 

 half of the New World. In Canada, and in the northern parts of the 

 United States, innumerable great scattered fragments of rocks have been 

 described by Bayfield, Bigsly, Hitchcock, and others. In parts of Massa- 

 chusetts, according to Professor Hitchcock f Report on the Geology of J, 

 boulders seem to cover the whole face of the country. Further south- 

 ward we hear from Mr. Rogers {Report to Brit. Assoc., vol. iii.) that boulders 

 are common over the great valley which crosses Pennsylvania, Maryland, 

 and Virginia (lat. 36° 30' to 42°) : and likewise in the states of Ohio, 

 Kentucky, and Indiana, which are in nearly the same latitude. Mr. 

 Rogers having described some blocks of sandstone at Washington and on 

 the Susquehanna, which must have come from some distance northward, 

 adds that " Drake in his picture of Cincinnati (39° 10') mentions large 

 masses of granite in that part of the Ohio, resting on the ordinary finer 

 diluvium. The nearest granite to the north is at least one hundred leagues 

 distant; while no primary rock occurs south or east, within even a much 

 greater limit." He then proceeds, " We are reminded here of the great 

 detached blocks, which strew the plains of northern Europe, and the ex- 

 planation suggested, that they have been carried there upon floating ice j" 

 and concludes with the important remark, that Mr. Conrad, who has ex- 

 plored the state of Alabama (30° to 35°) was never once able to perceive 

 a boulder upon its surface. It would hence appear that 36° 30' is the 

 southern limit of the dispersion of erratic blocks in the United States ; 

 and these are spoken of, as having come from the north. Therefore, there 

 is no occasion to suppose that the ice, in which by the theory they are 

 believed to have been embedded, was formed in so low a latitude as that 

 here mentioned ; and at present, in the southern hemisphere, icebergs are 

 drifted to latitudes, though not formed in them, nearer the tropic than 

 36° 30'. In Europe I cannot hear of erratic blocks having been found 

 further south than the southern flanks of the Alps, in lat. 45°; and Hum- 



